reset security questions

You need to set up two-factor authentication or contact Apple's Account Security team. To reach them, click here or here and pick a method; if you can't use any of those listed, choose one from this link.

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Do not try to sign in or change your security questions for a full 24 hours. After 24 hours use a device and Wi-Fi you’ve used to sign into the Apple ID with before and try resetting your security questions one more time.

If this still doesn’t work your next option is to try to enable to factor authentication following Two-factor authentication for Apple ID - Apple Support